(CNSNews.com) - U.S. Attorney General Eric Holder says the Supreme Court decision on voting rights “has the potential to negatively affect millions of Americans across the country.”

Holder held a press conference Tuesday afternoon at the Department of Justice where he was critical of the court's decision earlier in the day.

“I am deeply disappointed with the Court’s decision in this matter. This decision represents a serious setback for voting rights – and has the potential to negatively affect millions of Americans across the country,” Holder said.

The court declared unconstitutional a provision of the Voting Rights Act that requires certain states with a history of discrimination at the polls to get approval from the Justice Department or a special panel of judges before they change their voting laws.

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The requirement, which was first enacted in 1965, cannot be used unless Congress can come up with a new formula that Chief Justice John Roberts said meets "current conditions" in the United States.

Holder said the federal court had cited the Voting Rights Act in recent decisions. “Last year, a federal court cited the value of the Voting Rights Act in blocking the Texas congressional redistricting map on the grounds that it discriminated against Latino voters. “

“The federal court that reviewed South Carolina’s photo ID law also noted the ‘vital function’ that the Voting Rights Act played in prompting the state to change how it will implement the statute in future elections so that it would no longer disproportionately impact black voters.”

The Attorney General said that the Department of Justice will continue to carefully monitor jurisdictions for voting changes that may hamper voting rights.

“Let me be very clear, we will not hesitate to take swift enforcement action – using every legal tool that remains available to us – against any jurisdiction that seeks to take advantage of the Supreme Court’s ruling by hindering eligible citizens’ full and free exercise of the franchise.”